Explosive blast absorption

ABSTRACT

An explosive blast absorption barrier, comprising a plurality of layers including a front layer and at least one further layer which comprises a recess forming layer providing a plurality of conical or pyramidal tapered recesses, each tapering from a wider opening at a surface distal from the front layer to a narrower end, each tapered recess being at least partially filled with a mixture of particulate matter and a gel.

This invention relates to explosive blast absorption. In particular it relates to a system comprising a barrier absorbing the effects of blast waves.

It is a requirement to protect structures and buildings against the effects of blast waves caused by an explosion, for example. Typically methods of achieving this include hardening or strengthening the structure or using techniques to deflect the blast waves. All of these techniques can work reasonably well to protect the buildings and structures themselves, and often to protect persons within them. However, all hardened structures tend to reflect the blast wave and the reflective wave will then continue propagating until it meets another structure. This other structure might not be so well protected and the reflected wave may cause considerable damage and possible loss of life to and within the structure. Thus, if a particular building, say a Government building, is hardened to protect that building then an explosion occurring in the vicinity of that building may not harm the persons within that building but the reflective shockwave may harm persons in an unprotected building across the street for example.

In addition, extreme hardening of the walls of a structure, which will typically be a nationally or politically significant building, will tend to leave the windows as the most vulnerable component. This facilitates the likelihood of their failure with the potential for lethal shards of glass to pass into the building and, due to the negative phase produced by the blast, also to the surrounding exterior environment.

The present invention arose in an attempt to provide a system which absorbs rather reflects a blast wave.

In a first aspect the invention provides an explosive blast absorption barrier, comprising a plurality of layers, including a front layer and at least one further layer which comprises a recess forming layer providing a plurality of tapered recesses, each tapering from a wider opening at a surface distal from the front layer to a narrower end, each tapered recess being at least partially filled with a mixture of particulate matter and a gel.

The particulate matter is most preferably sand. The gel may be formed from a gelling agent such as gelatine and water or be a synthetic material.

The mixture is typically such that the particles are held within the gel material and set within each tapered recess.

The tapered recesses are most preferably conical or square pyramidal shapes.

The recess-forming layer may be of a pulped paper material. Typically, in the UK, material of this type is used for the formation of containers for storing eggs for consumption.

In preferred embodiments, at least two recess-forming layers with the particulate matter/gel mixture are included.

Each recess-forming layer may be mounted upon a support layer. This might typically be a corrugated card material.

The barrier may comprise two or more such recess-forming layers, each separated by a support layer, typically with at least one air gap between layers. A sacrificial trim or external panel may form part of the barrier, positioned at a point that is likely to be closest to the blast centre.

In elements of the invention, the recess-forming layer in effect forms a tray or containment element for the sand/gel mixture. It is therefore shaped to attempt to modify a pressure wave which propagates to it. The angle of incidence of a blast wave to the recesses may be around 42°. Preferably it is made of a material such as pulped paper and other material and may contain a flame retardant such as Borax which will allow it to be substantially non-combustible. It may therefore be formed from a slurry of paper and water in the same way as an conventional egg box. Other components may also have flame retardants.

The gel material most preferably contains water mixed with a gelling agent such as gelatine. In addition to being a material for retaining the sand particles it is also an important element in its own right and can absorb heat generated from an explosive event, converting this to steam and water vapour under heat and pressure and thus serves to dissipate some of the energy of the blast as well as acting as a retardant. It forms into a gel and provides for a mixture, with the sand or other particulate matter, that is malleable in order to take on the form available from the profile of the substraight.

The sand or other particulate material is moulded with the gel material and will be compressed with this into the recesses within the recess-forming layer. Each particle has a mass and requires energy to be moved and separated but also acts as a retardant. When mixed with the water/gelatine mixture this becomes malleable and can be formed into the recesses in the substraight as described.

Thus, in embodiments of the invention, the effect of a blast is to act on each of the many particles in each recess. Each of these absorbs a small part of the total blast wave power. Whilst the particles themselves may be ejected, relatively small particles of less than 2 mm, preferably less than 0.9 mm in diameter, have minimal lethal impact and, if coming into contact with a human body, are unlikely to lead to more than superficial damage or perhaps non-permanent scratching of eyes etc. Sand is generally defined as between 2 mm and 0.0625 mm in diameter so is a suitable and convenient material.

Clearly, the more particles in each recess the better, as each one absorbs a small amount of blast energy.

In a further aspect the invention provides a method of protection, a structure comprising mounting a barrier as described between the structure and a region where a blast may originate from, such that the barrier provides a sacrificial blast absorption barrier.

Embodiments of the invention will now be described, by way of example only, with reference to the schematic accompanying drawings, in which:

FIG. 1 shows an exploded view of components of an explosive blast absorption system;

FIGS. 2 to 7 show a cross section through the system illustrating propagation of a blast wave,

FIG. 8 shows a cross-section through the recess-forming layer, and;

FIG. 9 shows the cross-section of a tapered recess.

FIG. 1 shows the components of an explosive blast absorption system. Note that it shows one embodiment and in practise not all embodiments will include all of the layers shown in FIG. 1.

The system of FIG. 1 provides a barrier which might be a floor, inside or outside a building, a wall or a cover for a wall, a platform, a ceiling or roof, or a barrier mounted underneath a ceiling, floor or roof, a protective barrier protecting any structure, e.g. wrapped around a mast, a barrier for protecting an underground tunnel or structure such as a fuel container, bunker or munitions silo, or have many other uses.

It comprises a first layer which is generally a sacrificial trim/exterior panel and which may be flooring.

The next layer may be a non-flammable foam filing layer 3.

The next layer comprises a first one of two layers 4 which each form a plurality of tapered recesses (e.g. pyramidal or cone shaped), or triangular or other shaped channels, which are arranged to have wider openings further from sacrificial trim 2 and narrower ends (typically closed ends) which are closer thereto. They are therefore termed “recess-forming layers”). This may conveniently be formed, as is shown in the schematic FIG. 1, by using a structure of the type generally used to hold eggs for example, which may be made of pulped paper, or alternatively of cardboard or other material such that it may be able to disintegrate. Trials used commercially available egg boxes. However, specifically made components will generally be used in practice, and these may, but not necessarily, have recesses just on one side, being planar or otherwise formed on the other side.

These recess-forming layers each have a plurality of elements shown as 5 which are formed by a mixture of sand or other particulate matter, a gel (e.g. gelatine) and water. The gelatine and water forms a gel which, when mixed with the sand, form a malleable paste which can be pushed into the recesses 4 a of each layer 4. This may be done by inverting layer 4, filing each recess with the mixture and then allowing this to dry, when it will partially set to a sufficient level that when the layer is upturned, each pyramidal cone 5 is retained in place and does not fall out.

This component, when filled with sand/gel mixture 5, is then placed upon element 6, which is a support panel and which may be formed of corrugated card or otherwise. By making it of corrugated structure this provides further resilience and thus further blast absorption.

Note that the layer 4, which holds the conical elements 5, may have a substantially planer or otherwise formed upwards surface and may preferably just have the recesses formed in its lower surface. This is shown in FIG. 8.

Underneath panel 6 is a further typically similar panel 6′. However this need not necessarily be identical to panel 6. The two panels 6 and 6′ are separated by spacers which allow an air gap to be formed between them. The air gap is shown at 7 in FIG. 2. It may be of depth around 50 mm in some embodiments but could vary. Underneath panel 6′ is a further tapered recess-forming layer 4′ which has the same effect as layer 4 and has recesses in its lower surface which house further sand/gel cones 5. Finally, a further layer 9 is applied under layer 4′. This may again be of corrugated card and may be of more “heavy duty”, (i.e. thicker, have more layers, be made of a heavier duty material or otherwise) and panels 6 and 6′ forms a base panel.

Note that where the term “underneath” is used this is relative and applies when the barrier is used as a flooring. Clearly, if it is used other than “horizontally”, e.g. as wall material, or as a roof material, then the panels will not be relatively underneath each other in the same way.

Note that, however apart from at least one layer with the particle/gel mixture in recesses of this, the other components may be optional or any combination of them may be used in different embodiments.

The sacrificial layer and/or sand/gel layer (otherwise known as a containment tray) may be formed of sand or other particulate matter itself. Thus, that it may be made from said particles which are adhered together using a relatively strong adhesive and which can deconstruct under high pressure without causing lethal shrapnel. It may be formed of non-flammable fibrous elements such as nylon, resin materials or otherwise, most preferably of non-sharp elements. In addition, the sacrificial layer 1 may be made to have focused weak points to guide the pressure wave towards the centre of the system. This may be done by radially strengthening the layer from the centre, i.e. providing radial thickening ribs or otherwise or by making the layer stronger at its edge and weaker or progressively weaker towards its centre. Alternatively, a weaker portion can be formed at its centre and radially outermost parts will be strengthened. The strengthening can be done by making the strengthened part thicker, using a stronger adhesive on this, or otherwise.

If the tray is made of an adhesive sand it might be able to be formed in one forming operation with the conical inserts 5, by using with two types of sand, a first type which is more firmly bonded together to form the trays themselves and a second type which is mixed with the gel to form the pyramidal inserts.

Note that although sand is a preferred material, any particulate material can used. It is preferably one which is smaller than around 0.9 mm. Particles of greater than this size (coarse sand) might be liable to cause injuries such as eye injuries, so although usable, might be less preferred so that damage to a person, caused by the particles themselves being acted upon by the blast wave and impinging upon a person, is minimised and non-lethal.

The system, according to the present invention, forms a light weight, potentially portable, blast mitigation/absorption system. As described, the most significant components are the mixture of sand (or other particles), gelatine (or other gel forming agent) and water (or other liquid) which are formed in tapered recesses in recess-forming layers or trays and which will generally be mounted between support panels. An external sacrificial layer provides a surface upon which a person may walk, or forms the visible surface of a wall or other covering.

The system allows the destruction of its constituent parts in order to absorb energy from a blast wave. The system is designed to deconstruct by the blast loading, returning as far as possible to its constituted particles, e.g. sand particles, which are essentially inert and will not fragment into a form that is dangerous to persons or damaging to structural components. Thus, the energy of the blast is used in undergoing destruction of the barrier in a multi/micro ergonomic manner and thereby absorb the blast.

Referring again to the drawings and now to FIG. 2 onwards, the effect of the absorption system is schematically shown. Each of these figures shows a schematic cross sectional view of a barrier as shown in FIG. 1 mounted upon a structure 11 to be protected. As described, this may be flooring, road surface, the wheels of a vehicle, a ceiling or many types of structures such as wrapped around masts buried underground or perhaps under loading bays used to protect fuel depots, fuel storage areas, grain or food containers or many other applications.

As shown in the figures, a barrier B is placed above, or protecting a structure 11 to be protected so it may be stood off from this by a region 10 which may be a foam region, to provide more protection or which may be an air gap, in which case suitable spacers will be used (not shown) to space the barrier from the structure 11. Alternatively, it may be placed directly upon the structure.

As one example, each recess 4 a (otherwise known as a cell) may contain approximately 2.5 cc of a sand/gel mix. The recesses need not be filled totally to the “brim” with the sand/gel mix. If we assume 8,000 grains of sand per cubic cm (cc) then each cell contains around 20,000 grains of sand. Each grain will have an average 4 points of adhesion, giving 80,000 micro breeches of adhesion for the blast wave to overcome per cell. In one example, 540 cells are provided per square metre in tray/substraight 4 and this equates to 43.2 million micro breeches per square metre. Each cell weighs around 0.020 Kg which is equal to about 11 Kg per square metre in the system. If the barrier is in total 100 mm thick from layers 1 to 9 then an explosive blast wave, normally travelling at say 6,000 m per second, will complete the traverse in 6 milli-seconds. FIGS. 2 and 3 show the ongoing blast. FIG. 2 shows the situation before the blast impinges.

FIG. 3 shows the situation when the pressure wave starts to enter the system and begins to disperse the first layer 2-3 of the components the elements 5 in the first chamber collapse, dispersing the contents into the air gap region 7. Thus, first board 6 has been breached.

FIG. 4 shows the blast wave entering the air space between the first and second chamber, carrying the accumulated debris (sand etc) from the first chamber with it and dispersing this in a lateral manner, seeking the path of least resistance.

FIG. 5 shows the blast wave entering the second chamber and again compressing the conical element disbursing these and thus more debris starts to build up.

FIG. 6 shows the blast wave having travelled through the system having collapsed both sets of the sand/gel mixture in layers 4 and 4 a.

FIG. 7 shows the final stages of the blast wave's movement through the system, breaching the final support board 9 and releasing debris into the void 10 between the barrier system B and the structure 11 it is protecting.

In one test a 100 mm deep barrier system achieved an approximate reduction of 80% of blast pressure using the parameters described above.

The embodiments shown in FIGS. 2 to 7 show where two layer/container trays are provided, each holding a number of sand/gel mixture. This may be mounted such that they are in antiphase with another. See FIG. 2, for example, where the peak of the tapered recesses in top most tray 4 coincide vertically with the trough of the ones in the second tray. This enables material released from the first tray to travel down the sides of a tapered recess of the second tray, thus improving blast absorption.

Note that instead of the non-flammable form filing layer another air gap may be provided.

The tapered recesses may have curved closed ends rather than coming to a point. They may also have flattened closed edges (generally frustoconical). However, having a sharp angle at the other end helps to improve blast absorption.

Sand is generally defined by geologists as having particle size (diameter) between about 0.0625 mm ( 1/16 mm) to 2 mm. However in some embodiments gravel (size>2 mm) or silt (<0.0625 mm) may be used. Sand is preferred however.

Instead of conical or pyramidal shapes, the tapered recesses may be elongate channels having tapered sides, eg having a triangular cross-section.

FIG. 9 shows a recess which has an angle such that a blast wave arrives at an angle of incidence of around 40° (i.e. when the blast wave travels generally perpendicularly to the planes of the panels such as panels 2, 4, 6, etc). This is found to be dissipated energy most effectively however other angles may be used. 

1. An explosive blast absorption barrier, comprising a plurality of layers including a front layer and at least one further layer which comprises a recess forming layer providing a plurality of conical or pyramidal tapered recesses, each tapering from a wider opening at a surface distal from the front layer to a narrower end, each tapered recess being at least partially filled with a mixture of particulate matter and a gel.
 2. An explosive blast absorption barrier, as claimed in claim 1 wherein the particulate matter is sand.
 3. A barrier as claimed in claim 1 wherein the recess-forming layer is of a pulped paper material.
 4. A barrier as claimed in claim 1 wherein the recess-forming layer is formed of a particulate material.
 5. A barrier as claimed in claim 1 comprising at least two of the recess-forming layers, spaced apart from each other, and each having particulate/gel material within their respective conical or pyramidal recesses.
 6. A barrier as claimed in claim 1 wherein each of the recess-forming layers are mounted upon a respective support layer.
 7. A barrier as claimed in claim 6 wherein at least one of the support layers is of a corrugated card material.
 8. A barrier as claimed in claim 1 comprising at least two recess-forming layers having conical or pyramidal recesses at least partially filled with a mixture of particulate matter and a gel, each of these being separated by a support layer, and at least one air gap between at least two of the recess forming layers.
 9. A barrier as claimed in claim 1 wherein the outer layer is a sacrificial trim or external panel mounted closest to a region where an explosive blast is expected to originate from.
 10. A barrier as claimed in claim 1 wherein the conical or pyramidal tapered recesses are mounted such that the angle of a blast wave from an expected blast position is around 42°.
 11. A barrier as claimed in claim 1 wherein at least one of the recess-forming layers includes a flame retardant material.
 12. A barrier as claimed in claim 1 wherein the gel comprises water mixed with a gelling agent.
 13. A barrier as claimed in claim 1 wherein the recess-forming layer is formed of a mixture of particulate matter and an adhesive.
 14. A barrier as claimed in claim 1 wherein the particulate matter forming the recess-forming layer is a sand material.
 15. A protective structure for forming a floor, wall, ceiling or structure mounted around an area to be protected from blast, comprising a barrier as claimed in claim
 1. 16. A method for protecting a structure comprising a mounting a barrier as claimed in claim 1 between the structure and the region where a blast may originate from, such that the barrier provides a sacrificial blast absorption barrier. 